The long-term objectives are improved treatment results in patients with hemifacial microsomia, and the application of successful treatment procedures to other types of craniofacial anomalies (i.e. syndromes involving cranial and midface malformations). At the present time, any desired increase in length of an underdeveloped mandible can be achieved with long-term stable results. It is also possible to achieve growth by bone appoisition of a lengthened structure. At this time we are not able to apply the pertinent biological principles to the anterior part of the mandible or to other bones in the craniofacial skeleton or the rest of the body. It has not yet been clarified which muscles are essential for the development of the various parts of the bones. This proposal has two specific aims: 1. Determine changes in size, volume and neuromuscular properties of congenitably underdeveloped muscles in response to altered skeletal morphology. 2. Determine if recruitment patterns for mastication differ from the normal in; 1) subjects with missing joint structures, but presence of a condylar process and lateral pterygoid muscles (Type I) and in 2) subjects with absence of the condylar process and probably absence of the lateral pterygoid muscles (Types IV and V). Electromyographic data obtained by surface electrodes from jaw elevator muscles during rest, voluntary jaw movements, and during mastication will be assessed before and during stages of treatment. CT scan techniques will be utilized to assess muscle volume, cross-sectional area and length before and after mandibular respositioning. Further undrstanding of the association between the neuromuscular system and the skeletal components should result from testing the hypotheses formulated in this proposal.